1. Field
Embodiments of the invention relate to power devices, such as power switching devices or chips.
2. Description of the Related Art
Power devices are semiconductor devices that can be used as switches or rectifiers in power electronic circuits. Examples of power devices include the power diode, thyristor, power metal oxide semiconductor field-effect transistor (MOSFET), bipolar junction transistor (BJT), and insulated gate bipolar transistor (IGBT).
Power devices may be divided into those that are two terminal devices and those that are three terminal devices. The state of two terminal devices, such as diodes, is completely dependent upon the external power circuit they are connected to. The state of three terminal devices, such as a transistor or thyristor, is not only dependent upon their external power circuit, but also upon the signal on their driving terminal (i.e., gate or base).
In addition, power devices can be majority carrier devices (e.g., MOSFET) or minority carrier devices (e.g., BJT). Majority carrier devices use only one type of charge carriers, while minority carrier devices use both types of charge carriers, i.e., electrons and holes. Majority carrier devices may be faster, but the charge injection of minority carrier devices allows for better on-state performance.
IGBTs have replaced the bipolar transistor in power applications, and the use of power modules where several IGBT dice are connected in parallel is applicable for power levels of several megawatts. IGBT has the advantage of being a minority carrier device with good on-state performance, and simultaneously having the high input impedance of a MOSFET so that it can be driven on and off with a low amount of power.
Thermal resistance is an important parameter for power devices. Semiconductors do not perform well at high temperatures, but, because of large current conduction, power semiconductor devices will heat up. Accordingly, power semiconductor devices need to be cooled by the continuous removal of heat. Packaging and heat sinks provide a way to remove heat from power semiconductor devices by conducting the heat to the external environment. As a result, large power devices also have large die and packaging surface areas and lower thermal resistance.